XML External Entities (XXE) Back
According to Wikipedia,
An XML External Entity attack is a type of attack against an application that parses XML input. This attack occurs when XML input containing a reference to an external entity is processed by a weakly configured XML parser.
Because most XML parsers are vulnerable to XXE by default, developers should ensure that applications does not have such a vulnerability.
According to OWASP, the XML External Entities (XXE) main attack vectors are:
- XML processors where hackers can upload XML or hostile content in a XML document
- vulnerable code
- vulnerable dependencies
- vulnerable integrations
If you want to know more about examples of XXE, you can check here. And to prevent XXE, some ways are advised by OWASP:
- Use less complex data formats such as JSON, and avoid serialization of sensitive data if possible.
- Patch or upgrade all XML processors and libraries in use.
- Disable XML external entity and DTD processing in all XML parsers in the application, as per the OWASP Cheat Sheet "XXE Prevention".
- Implement positive server-side input validation, filtering to prevent hostile data within XML documents, headers, or nodes.
- Verify that XML or XSL file upload functionality validates incoming XML using XSD validation.
- SAST tools can help detect XXE in source code. Note: code review is the best alternative in large, complicated applications with many integrations.
If you want to prevent outside the XML processor itself, you can consider using:
- API security gateways.
- Web Application Firewalls (WAFs).